U.S. Pat. No. 4,123,075, owned by the assignee of this invention, discloses a jaw chuck which has proven highly desirable for use at high rotative speeds. This chuck uses axially movable wedges for effecting radial gripping engagement of the jaws, with the jaw assemblies being confined within a continuous surrounding cylindrical housing which structurally reacts with the jaw assemblies for resisting the centrifugal forces imposed on the jaws. This prior chuck hence maintains a proper gripping engagement with the workpiece without requiring complex linkages or movable weights for effecting centrifugal balance.
However, the aforesaid chuck is of the "pull" type, that is, the actuator wedges are pulled axially rearwardly away from the jaw-carrying front face in order to displace the jaws radially inwardly into gripping engagement with the workpiece outer diameter. While jaw chucks of this general type have conventionally utilized a pull-type actuator, nevertheless it has been observed that this type arrangement possesses several disadvantages, as follows:
1. The external load imposed on the workpiece is spaced forwardly from the jaws, and hence this load creates an axial tilting moment which creates a tendency for the jaws to open. The pull-type actuator wedge, which causes inward radial displacement of the jaws for gripping engagement with the workpiece, also imposes an axial tilting moment on the jaw which acts in the same rotational direction as the tilting moment created by the external load, and hence these two tilting moments tend to reinforce one another so that secure gripping of the workpiece is made more difficult. This also often damages the workpiece due to the outer corner or edge of the jaw "biting" into the workpiece.
2. The wedge actuator is moved rearwardly to activate the jaws, and since the jaws are disposed closely adjacent the front face of the housing, the actuator wedge is normally in slidable engagement with the respective jaw carrier throughout substantially the full axial extent thereof only when in a non-activated position. The axial extent of engagement between the wedge and jaw carrier decreases as the jaw is displaced radially inwardly, so that the wedging engagement between the activator wedge and jaw carrier normally occurs solely adjacent the rearward side of the jaw carrier when the latter is grippingly engaged with the workpiece. This thus minimizes the desired force-transfer area between the wedge and jaw carrier, and also results in the activating force being positioned greatly off-center, whereby the force-transfer arrangement relative to the jaw carrier is less than optimum.
3. The aforesaid force-transfer arrangement between the wedge and jaw carrier normally results in some of the components within the activator and jaw assemblies being subjected to tension stresses, and hence the overall assemblies are more subject to breakage or failure.
Thus, this invention relates to an improved jaw chuck which overcomes the above-mentioned disadvantages. More specifically, this improved jaw chuck permits the jaws to be radially inwardly moved for gripping engagement with the outer periphery of a workpiece, but the jaw assemblies are activated by a push-type actuator assembly which maintains the jaws in gripping engagement with the workpiece, while at the same time this improved chuck is still highly desirable for use at high rotational speeds in view of its ability to maintain effective gripping between the jaws and the workpiece in resistance to the centrifugal forces imposed on the jaw.
In this improved jaw chuck, the activating wedge moves forwardly into a more intimate wedging relationship with the jaw carrier to effect inward displacement of the latter for gripping the workpiece, such that the activator wedge is in secure engagement with the respective jaw carrier over substantially the full axial extent thereof when the jaw grippingly engages the workpiece. The forces imposed on the jaw carrier are thus more effectively centered so as to provide for more optimum force-transfer through the jaw assemblies to the workpiece. This arrangement also results in the actuator wedge imposing on the jaw carrier an axial twisting moment which effectively opposes the external moment imposed thereon by the workpiece, so that more effective gripping of the workpiece is achieved. This improved arrangement also results in the actuator and jaw assemblies being subjected substantially solely to compression forces when the jaws grippingly engage the workpiece, whereby the possible occurrence of a structural failure is greatly minimized.
In the improved jaw chuck of this invention, there is provided an inner sleevelike housing which, at the forward end, is provided with radially extending T-shaped slots which slidably accommodate the jaw assemblies, which jaw assemblies have gripping means for engaging the exterior periphery of a workpiece. The inner sleevelike housing is totally surrounded and fixedly connected to an outer sleevelike housing which overlaps the outer ends of the slots. A push-type activator is disposed adjacent the rearward end of the inner sleevelike housing and is axially slidable relative thereto. This activator includes wedges which project axially forwardly and are slidably and wedgably engaged with the jaw carriers for effecting radial displacement of the latter. The wedges have the outer peripheries thereof axially slidably supported on the inner periphery of the outer sleevelike housing. The wedges are of a T-shaped cross section and are slidably engaged with similar T-shaped grooves which extend axially through the jaw carriers, which wedges and grooves are sloped at a small angle relative to the axial direction as they project toward the front side of the chuck.
The objects and purposes of this invention will be more apparent after reading the following specification and inspecting the accompanying drawings.